Application on Square-base Coolers

Without question, the most dominant mounting shape for CPU coolers is the square base. The formula is very simple: the most effect method to cover a square processor and integrated heat spreader is to match it with a square cooler base. Science is simple that way, right? While I have seen some examples of glass slides being used to demonstrate the spread pattern of Thermal Interface Material under ideal conditions, I seldom find myself with two perfectly flat and non-porous surfaces.

If only it could be so simple in the real world of retail thermal cooling solutions. Since the ultimate end-goal is to have the integrated CPU heat spreader surface contact metal-to-metal with the coolers base, it's necessary to have a perfectly flat and smooth contact surface at both ends. This usually means lapping the processor and cooler surfaces with wet-sanding paper and polishing compounds, along with a few hours of effort. Some manufacturers try to achieve this right out of the box, while others completely ignore thermal dynamics and finish their mounting surface with stone grinding.

Thermalright is probably the biggest offender in the category of poor factory surface finishes, which is ironic if you consider the loyal fan-base who adore their products without question. The image below is of a brand new Thermalright HR-01 CPU cooler (the 120 eXtreme was pictured on the first page of this article), right out of the box. You will no doubt notice that it doesn't have a very smooth finish... which would have to be be polished before I could continue because thermal paste didn't seem to spread very well with so many tracks running across the surface.

Since Thermalright products are generally ground flat and level, albeit far from smooth, they can accommodate a wide range of application methods. Ideally my article would have been made better if I had two perfectly flat real-world surfaces to work with, but time and project needs keep me from this goal at the moment. If I didn't have the Noctua NH-U12P tied-up with another project, I would have just used it for this segment. For now I am working with the tools I have available to me, and not the tools I wish I had... so expect a rewrite at some point.

The first thermal paste application pattern to test was the single drop. One single drop of TIM was placed directly in the center of the mounting base surface, roughly half the size of a BB.

Once all four corners of the cooler were depressed, and a bit of extra force pressed down in a circular motion to ensure maximum contact, the entire unit was removed an photographed. My results show that the single drop pattern spread out to reach only two edges of the CPU, while falling short of the other two sides. This could be attributed to several variables: poor mounting system and pressure, uneven mounting surface on the cooler or processor, and perhaps even a warped motherboard.

Next up was the single line pattern, which used a small half-inch long application of paste down the center of the coolers mounting base. The direction of the thermal paste was perpendicular to the direction of the surface grain (which was still present after an hour of effort).

Perhaps I didn't use enough thermal paste, because it appears as though the pattern might have worked with a slightly shorter yet thicker application of material. With some additional trail and error testing, this application pattern may prove successful for some coolers, but even after another retest using a bit more material there was still less coverage than the single drop method.

Since the one line pattern didn't quite reach out to the edges, I figured that two lines might do the trick. Spaced apart at an interval of 1/3 the width of the processor, these two lines were slightly shorter than the single line pattern and equalled half the width of the processor in length.

One of the fears I hear about most with this method is that air may get trapped in the middle. However, one look at the image below and I can safely dismiss this potential problem. After the cooler was lifted, I discovered that the two line pattern was able to reach all four edges of the CPU. It seems that this method could have some real world application if correctly applied.

It took some additional cold tests for me to get the amounts correctly tuned. After the retest results (not pictured), the best ratio I found was using line lengths equal to the distance between the lines; or roughly 1/3 the width of the processor.

Next up was the cross method of applying thermal paste to the coolers mounting surface. Since two lines worked well, perhaps overlapping them would have an improved effect? I have not personally used this pattern in my own systems, but other web sites have claimed that it can work.

After a few test applications, the image above is the best coverage I could get. Plenty of material covers the surface, but there are clear signs that too much TIM has reached the edges. Again, the disclaimer here is that this pattern might work for your setup, and every application is different. In my tests however, I wanted more uniform coverage and the cross method took some practice before it could meet my needs.

In the image above my line length was too long, measuring 2/3 the width of the processor. With additional cold tests (not pictured) I learned that lines of the same thickness but only 1/3 in length did a better job and kept the material amounts in check.

Last but not least is my own personal method. Not to harp on the subject, but you don't want a thick layer of thermal compound between mounting surfaces. There isn't a magic thickness to suggest, since different surface finishes will require different amounts of material to fill them. If both surfaces were as smooth as glass though, I would need less than half the material used in the above tests to reach the same coverage.

So when I come across a very rough yet level surface, I prefer to smooth out the material using a rubber finger cover or plastic bag in directions opposite to the grain. This does an excellent job of filling in the groves and scratches, and can be used in combination to the above methods as a base. In cases where I use both methods, the "base" coat is extremely thin and the metal beneath it is still visible.

However if I choose to use just the one layer, I leave a coat just barely thick enough to hide the metal surface below it. This method doesn't leave enough material to spread out across the surface and press out bubbles as it bleeds, so the cooler must not be placed flatly onto the processor surface to begin with. Instead this method must be carefully placed down at a slight angle as it is compressed, similar to how you might apply an adhesive sticker to avoid bubbles.

I will admit that there's plenty of room for additional testing and improvement in this section, which I forewarned would most likely be the case for an upcoming edit. Please take this information for what it's worth, because we did still discover a few application patterns that would never work well under any circumstance.

In our next section, careful consideration is given to the application of thermal paste on the new Heat-pipe Direct Touch cooling products.

Benchmark Reviews invites you to share your comments and suggestions for this topic in our Discussion Forum.

Comments

Thanks Benchmarkreviews for this is a very informative article.This kind of quality reviews makes it a lot easier for enthusiasts, like me, which do not have much resources for us to try such tests.Thanks again... and i hope for more quality reviews from you guys..

Thank you for researching and publishing your work on applying thermal paste. I don't have a HDT heat sink, but the design is exactly the same as the Cooler Master Hyper 212 Plus Direct (blah blah the name is sooooo long).

Thank you for a well written and presented article. I recently purchased a Xigmatek 'Red Scorpion' cooler to replace my stock Intel LGA775 cooler. Now I know how to best apply the paste! Also, my Red Scorpion was supplied with the white thermal paste, thanks again for explaining what these compounds are made from. I will throw out the white paste and get some that has a high silver content.Cheers!

Olin, under the section "Heatpipe Directional Orientation" are you stating that it is better for the CPU cooling fan to point toward the top of the case, rather than front to back? I would think this would be true for PC cases that have the PSU mounted on the bottom of the case, and have a fan at the top, blowing outward. The new Lian Li PC-A04 case is a perfect example of this. Can you comment? (Thanks!) Perhaps a picture would be helpful here.

In further reading, I realize that I didn't catch what you were explaning. I do understand what you are saying now. But my additional point/question is still relevant. If you take a look at the Lian Li PC-A04 case, wouldn't it make sense to re-orient the CPU cooler towards the top of the case? (They actually do not include a rear fan.) I would think that a vertical orientation of the heat pipes, along with a bottom to top fan direction would be optimal, considering that hot air rises.

As you've stated, heat rises. Additionally, despite capillary action gravity still affects the heat-pipe fluid. It's best to orientate the heatsink so that heat-pipes are either level or collecting fluid at the base.

Assuming that "BB" size is equal to 4,57 mm and "BBB" to 4,83, and as "LGA775" is 37,5 x 37,5 millimetres, and on the picture with the peas the pea is approximately 1/3rd of the diameter which results in 12,5 mm. which is 1,25 cm I do arrive to the conclusion that in you country agronomy is really advanced. In my country peas are generally around half a centimetre, which make them BBB size and almost BB size. So, in conclusion, the communityis still as keen as it thought, or in other words, it is not mistaken - your peas are mistaken ( they are really f***** up ;) ). I do hope this is cleared out, and I do hope that somebody confirms the size of the peas on the picture, based on my assumptions!

These were frozen peas, and they are slightly larger than a pencil eraser. In the photo, that bit of thermal paste was roughly half the mass of a BB, and it covered the entire contact base on an old LGA775 cooler.

The peas being referred to by the term "the size of a pea" (and in the fable "The Princess and the Pea") are the peas you make pea soup out of, which are dried peas. Dried peas are much smaller than frozen peas, about the size of the TIM you used in the now infamous frozen peas picture. But instead of peas, I had heard the amount to place was the size of a rice grain which also works and is less confusing.

On a different subject, I would liked to have seen the results of mounting the square cooler that you did a thin, even spread of TIM on. How did it look when removed?

Also I would like to see heat readings from all these different application methods. While you may want one or the other spreads visually, how does that translate into actual practice? Could less coverage translate into a thinner layer that increases metal to metal contact, yielding better results than 100% CPU coverage but thicker layer? Inquiring minds want to know!!

^Where you have pipes on the heatsink base, there are tiny dips as the surfaces meet, the base is not 100% flat, therefore it is vital that you ensure these channels are filled with paste to properly conduct the heat away from the processorMoto

Hi Olin. I found your article to be extremely informative, thanks. I was wondering if you could shed some further light on whether or not failure to sand down an HDT cooler would make any significant difference for a pc that is never going to be overclocked at all. I would particularly appreciate your views on the Coolermaster Hyper TX3 cooler, which looks as if the the pipes are set too deep into the mounting base. See links below.

After having read your article, I have concluded that the two drops on the two centre partitions of the mounting base would be the best option for the Hyper TX3 cooler (to be used with an AMD Phenom II x6 1100T CPU), however, if sanding is not carried out, how would one deal with the space between the deeply set pipes and the CPU surface? Also, I have read that even merely touching the metal with a finger can cause grease and all kinds of particles to become stuck to it, so if sanding were to be carried out, how could one possible ensure that the cooler is thoroughly cleaned of all the residue from sanding? Thank you for any advice.